Coke derived from hydrocarbonaceous charge stocks and used for metallurgical purposes are priced inversely proportional to the sulfur content thereof. In some applications of metallurgical coke, acceptable sulfur levels are as low as 2 wt. % or even less. The sulfur contained in hydrocarbonaceous charge stocks utilized as coke precursors increases as the molecular weight of the hydrocarbon fraction increases. If the reduced crude from a typical Prudhoe Bay crude oil was coked in a low pressure coker, the sulfur level in the resulting coke would be about 2.8 wt. % which is unsatisfactory for metallurgical coke.
I have discovered that if a high recycle rate of desulfurized coker effluent is utilized, the yield of coke is increased and the sulfur in a Prudhoe coke, for example, would be reduced to at least 1.8 wt. %. The lower sulfur content would result because a greater portion of the coke would be derived from the lower molecular weight, lower sulfur gas oil boiling range fraction. According to the method of my invention, a high quality metallurgical coke may be prepared from high sulfur containing hydrocarbonaceous charge stocks.